Add availableForStore method to RingBuffer

cores/arduino/RingBuffer.cpp

@@ -67,6 +67,14 @@ int RingBuffer::available()
 		return delta;
 }
 
+int RingBuffer::availableForStore()
+{
+	if (_iHead >= _iTail)
+		return SERIAL_BUFFER_SIZE - 1 - _iHead + _iTail;
+	else
+		return _iTail - _iHead - 1;
+}
+
 int RingBuffer::peek()
 {
 	if(_iTail == _iHead)

cores/arduino/RingBuffer.h

@@ -40,6 +40,7 @@ class RingBuffer
 	void clear();
 	int read_char();
 	int available();
+	int availableForStore();
 	int peek();
 	bool isFull();